Impact of injection angle on the performance of a contra-rotating fan

This study investigates the effect of air injection on a low-speed contra-rotating fan, utilizing both experimental and numerical methods. Two injection rates, equivalent to 1.6% and 3.2% of the main mass flow rate at near-stall conditions, have been examined in this research. The results indicate that the latter not only enhances the performance of the stage but also alters its stalling pattern (shifting from what is known as wall-stall to blade-stall). Additionally, the impact of injection angle on the contra-rotating fan stage is explored. It is demonstrated that tip injection of air in the opposite direction to the front blade rotation increases fan stability, although it reduces the pressure rise coefficient. Conversely, when air is injected in the same direction as the front blade rotation, both stability and pressure rise coefficient improve, which contrasts with the behavior observed in conventional compressors and fans.